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Excitation Source: Tunable SR (UV –X rays)
Photon-out phenomena:
- Scattering (elastic, inelastic, resonant)
- Fluorescence (core-hole decay)
X-ray fluorescence (hard x-rays)
X-ray emission (soft x-rays)
Luminescence (UV-visible)
Auger (pseudo-photon)
De-excitation spectroscopy II:
Photon-in Photon-out spectroscopy
X-ray fluorescence (XRF)
X-ray emission (XES)
X-ray excited optical luminescence (XEOL)
Photon-in Photon-out Spectroscopy
hvex
XA
NE
S
Abs.
E
core
Edge
hvf
E
core
EF
Fluorescence Energy (eV)
XRF
X-ray fluorescence (XRF)
X-ray fluorescence: shallower core electron
(e.g. L shell) to deeper core hole (K) transition
XA
NE
S
Abs.
E
core
Edge
hvf
E
core
(Auger) Secondary
processes
EF hvop
Optical XAFS
Mono
XEOL
200 850
Wavelength (nm)
PLY
Mono
Ef
X-ray Energy (eV)
XES
X-ray emission (XES) and X-ray excited optical
luminescence (XEOL)
hvex
NBG defect
XES: valence electron to shallow core
XEOL: CB to VB & defects
Core level directly
below valence band
X-ray Fluorescence measurements
• Scintillation counter
• Ion chamber (Lytle detector) (with filters)
Nondispersive (no energy resolution)
Moderate energy resolution
High energy resolution
Solid state detectors (Ge, Si), order of 10 to102 eV
WDX detector (crystal monochromator) E/E ~ 800
Very high energy resolution
MiniXS (Jerry Seidler, U. of Washington)
E/E ~ 4000 5
X-ray Fluorescence properties of elements
Auger yield = 1 – FLY
FLY for low z elements
(C, N, O etc.) is << 1 %
Normal Fluorescence: Core-Core
XES: L or M = valence band
Resonant: Core-CB excitation
Ca:
Z= 20
X-ray Fluorescence:
X-ray photons in, x-ray photons out.
Results from the decay of a deep core
hole (e.g. K, or L)
Monitor the absorption spectrum using
fluorescence yield (FLY) → element
specificity
Detection Schemes
• High sensitivity, non-dispersive
Channel plate, Ion chamber
(solar slits, filters, e.g. Lytle)
• High sensitivity, moderate energy resolution
Solid state detector (e.g. Canberra 13 element
at PNC-CAT, Si drift detector at CLS)
Gas proportional counters (e.g. Fisher/Ohta)
• High sensitivity, more moderate resolution
Multi-layer Array Analyzer Detector (MAAD)
Log spiral detector (asymmetric Laue bent)
13 element detector
transmitted beam
specimen
KB mirror
PNC-XSD Microprobe
hvf
Photon Energy (eV)
2000 4000 6000 8000 10000 12000
Inte
ns
ity (
co
un
ts)
10
100
1000
10000
Ca Fe Cu
Zn
Ni
elastic
peak
Metals in mouse kidney tissue (hard X-ray)
XRF
Photon Energy (eV)
9000 9200 9400 9600 9800
FL
Y (
arb
. u
nit
s)
0
1
2
3
Photon Energy (eV)
8950 9000 9050
FL
Y (
arb
. u
nit
s)
0
1
2
3
Cu K-edge, mouse kidney (10 micron pixel)
quartz slide
Incident X-ray
hv =10 keV
Lu, soft x-ray [Phys. Rev. B, 58 (1998)]
20 element Multi-Array Analyzer Detector (MAAD)
[Ke Zhang et al. HD Technologies Inc. ]
Energy scan: elastic,
Ca K and K
E = 150 eV at Ca K
Ca
K, K
Schematic of an asymmetric cut
Si (100) wafer where in polar
Coordinate: r() = ae b,
b = tan [Khelashvili et al.
Rev. Sci. Instru. 73, 1534 (2002)]
Variable width
thickness
• Low sensitivity, good resolution WDX
(Rowland circle crystal optics)
LiF crystals (electron microprobes): 2-5 keV
[e.g. PNC-CAT]
Ge (3,3,3), Si (4,4,0): Fluorescence > 5 keV
• Low sensitivity, good resolution (< 2 keV)
Grating monochromator [e.g. BL 8.0.1, ALS]
Detection Schemes (continues..)
WDX from an electron microprobe
Wavelebgth
2.1 2.2 2.3 2.4 2.5 2.6
Inte
nsity
0.000
0.002
0.004
0.006
Photon Energy (eV)
5710 5720 5730 5740 5750 5760 5770
FLY
0.000
0.002
0.004
0.006
0.008
0.010
0.012
Ce L3-edge
Fluorescence
X-rays
Ce L
Ce L
Green Titanite
Brown Titanite
Ce L3 edge of Ce in Titanite: WDX detection
Ti K 1 4932 eV Ce L2 4823.0 eV
Ce L1 4840.8 eV Ce L1 5262.2 eV
0.06%
0.1%
Neither SS nor WDX detector will resolve Ce L from Ti K
But WDX can resolve Ce L nicely
Ce in Titanite: Microprobe using WDX
17
Titanite (CaTiSiO5,
sphene) is a common
mineral in mafic-felsic
igneous and meta-
morphic rocks, and it
is widely used for
geochronologic and
petrogenetic studies
American Mineralogist, Volume 98, 110–119, (2013)
K Fluorescence of MnO using Ge(333) and Si(440)
crystals (Rowland circle optics, S. Cramer X-25
NSLS, 2002)
2p
2s
3p
3s
3d
K (core-
valence)
emission
19
Dickinson et al. Rev. Sci. Instrum. 79, 123112 (2008)
3rd order2nd order10001000.31800 lines/mm, 5 m, resolution:
300 meV (at 1000 eV)
150 meV (O K-edge at 525 eV)
1200 lines/mm, 5 m, resolution:
100 meV (C K-edge at 275 eV)
600 lines/mm, 3 m, resolution:
50 meV at 90 eV
Very High Resolution Spectrometer
Cu 3p;
75eV+/- 10meV
RP~7,500
870mm
150mm
Ruling (center) = 2000 lines/mm
14o 0th order
130 mm X 25 mm
R = 4060 mm
Magnification 1.3
MERLIN at ALS:
Acceptance: ~33mrad (V) by 12mrad (H)
6mm by 15mm source
Uppsala University:
Source size: 6 mm x 60 mm
Grating: 1800 l/mm
Angle of incidence: 85 deg., inside order
Acceptance angle: 20 mrad x 50 mrad
h [eV]
75.25 10 meV
75.00
Source size: 6 mm x 60 mm
Grating: 1200 l/mm
Angle of incidence: 78 deg., outside order
Acceptance angle: 100 mrad x 50 mrad
10 meV
Courtesy of J.H. Guo
lsv
l
Source Grating
F
' = 10 mm / 20 mm = 0.5 mrad
= 2.5 cm / 5 m = 5 mrad
'XSource
Slit
Beam size (1994):➢ 1 mm at BW3 (HASYLAB) & X1B (NSLS)
➢ 100 mm at BL7.0.1 (ALS)
The beam size can be seen at 20 mm distance:
5 mrad x 20 mm = 100 mm
2 cm
100 mm
Intensity of X-ray emission Spectra
❖ Fluorescence Yield
➢ Photon hungry experiment
➢ Resonance enhancement
❖ Excitation➢ Synchrotron radiation
➢ Undulator (Linear, EPU)
➢ Monochromator
❖ Detection
✓ Diffraction efficiency of grating
▪ Blaze
▪ Grove density
▪ Surface quality
✓ Quantum efficiency of detector
▪ MCP (Photon cathode coating)
▪ CCD
✓ Beam spot size
✓ Solid angles to collected (slit size)
YBa2Cu3O6 YBa2Cu3O7-Guo et al., Phys. Rev. B 61, 9140 (2000)
XES + XAS : Bandgap determination
Guo, Int. J. Nanotech. 1-2, 193 (2004)
Band
gap
No
band
gap
85 90 95 100
0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
5500
6000
clean Si (100)
clean PS
dirty nanowires
dirty PS
clean nanowires
Files: .r01; Plot: Ian.opj
XES spectra of Si samples
Co
un
ts
Emission Energy [eV]
Si L XES: Si → Valence Band
SiNW
(as prepared)
XPS: Valence Band
SiNW
(HF)
L3,2-edge
as-prepared PS
clean Si(100)
as-prepared SiNW
clean PS
clean SiNW
SiNW (HF)
XES of Alq3
XES:PDOS (occupied) XANES:PDOS (unoccupied)
XES
XES
P.-S.G. Kim et. al. J. Elect. Spectros. , 901, 141(2005)
N
NO
OAl
N
O
- +
Glass
Indium Tin Oxide (ITO)
Hole transport layer
Electron transport layer
Emission layer
Ag/Mg
LightEmission
OLED (Organice Light Emitting Device)
XES of Alq3
XES:PDOS (occupied)
XES
P.-S.G. Kim et. al. J. Elect. Spectros. , 901, 141(2005)
XESXES
XPS: Caruso et al. Chem. Phys. Lett. 413 (2005)
HOMO, HOMO-1:
Mainly C character
XEOL: X-ray Excited Optical Luminescence
X-ray photons in, optical photons (UV, visible,
near IR) out.
Luminescence can be element and excitation
channel specific.
Monitor the absorption spectrum using the photo-
luminescence yield (PLY) element and
chemical specificity
XEOL - Conversion of X-ray energy into
optical emission
Core level
Recombination
via exciton
Recombination via bound exciton,
impurity and defect statesoo
UV
vis.
X-ray phosphorThermalization: electrons in
the CB, holes in VB
hv ~ Eo
hv >Eo
Elliot & Gibson
Solid State
Physics Haper
& Row, 1974
36
hvop
hvexPLY (l selected) XANES
Mono
XEOL
XA
NE
S
Abs.
E
200 850
Wavelength (nm)
CB
VB
EF
XAS and XEOL (Optical XAFS)
Edge
NBG defect
1050104010301020
Energy (eV)
520 nm
OL
ZB XAS
PLY
TEY
ZnS Zn L-edge
De-excitation, Energy transfer in nanostructures
Core leveloo
hv ~ Eo
hv ~>Eo
• Decay channels
• Attenuation of e and fluorescence x-
rays (thermalization) in the solid
yields secondary electrons (holes)
hvf
VB
core
Auger,
LVV
• Thermalization track is confined
(truncated) in nanostructures
Photon-in: Synchrotron Light
• Tunability → Element, edge,
excitation channel specificity
• High brightness
• Polarization
• Time structure
XEOL Techniques
Energy DomainXEOL: Luminescence induced by selected excitation photon energy (usually across an absorption edge)
Optical XAFS: Monitored with the optical signal
Time DomainLifetime: Synchrotron pulse Time-resolved (gated) XEOL: Luminescence within a selected time window between pulsesTime-gated Optical XAFS: Time window
40
Alternative: fiber optics,
spectrograph with CCD
detectors (e.g. Ocean
Optics QE65000)
XEOL: Experimental Layout
41
• Case studies
Si nanostructure
ZnS nanoribbons (crystal structure
engineering)
Soft matter
Alq3 (OLED materials)
2D – XEOL TiO2 nanowire
XEOL - Energy Domain
Photon Energy (eV)
1800 1900 2000 2100 2200 2300
TE
Y
0
1
2 Porous Si
Si nanowire
Si (100)
Si K-edge XAFS
42
Si L-edge XEOL (porous silicon)
Photon Energy (eV)
85 90 95 100 105 110 115 120
To
tal
Ele
ctr
on
Yie
ld (
ab
r.
un
its)
10
20
Porous Silicon
Si(100)
20 mA
5 mA
200 mA
500 mA
50 mA
Si L3,2
-edge
current (cm-2
)
Photon Energy (eV)1 2 3 4
Ph
oto
lum
ines
cen
ce (
arb
. u
nit
s)
0
200
400
600
a
b
a. ambient (H25)
b. HF refreshed
Porous Silicon
Excitation Energy: 100 eV
Wavelength (nm)
200 300 400 500 600 700 800 900
Ph
oto
lum
ines
cen
ce (
arb
. u
nit
s)
0
100
200
300
400
Excitation Energy
b
a. 100 eV
b. 110 eV
Porous Silicon
(ambient) a
Fig.1
Wavelength (nm)
200 300 400 500 600 700 800
Inte
nsity
(arb
. uni
ts)
1000
2000
3000
4000
5000
6000
7000
8000
9000
10000
11000
12000
460 nm 630 nm
530 nm
hvex
(eV)
1890
1867
1851
1847.5
1845
1842
1840
1838.5
1830
Wavelength (nm)
300 400 500 600 700
Inte
nsity
0
1000
2000
3000
40001847.5 eV
1842 eV
difference
curve
Photon Energy1840 1850 1860 1870
TEY
0
1
2
3Si K-edge
SiO2
Si
(a) (b)
Si K-edge XEOL of silicon nanowires
Phys. Rev. B 70, 045313 (2004) 43
Si nanowire
Photon Energy (eV)
1830 1840 1850 1860 1870 1880
Inte
nsi
ty (
arb
. un
its)
0
10
20
30
40
PLY zero order
TEY
FLY
630 nm
460 nm
530 nm
SiSiO
2
Si K-edge: PLY
Wavelength (nm)
200 300 400 500 600 700 800
Inte
nsit
y (a
rb. u
nits
)
1000
2000
3000
4000
5000
6000
7000
8000
9000
10000
11000
12000
460 nm 630 nm
530 nm
hvex
(eV)
1890
1867
1851
1847.5
1845
1842
1840
1838.5
1830
Wavelength (nm)
300 400 500 600 700
Inte
nsi
ty
0
1000
2000
3000
40001847.5 eV
1842 eV
difference
curve
Photon Energy1840 1850 1860 1870
TE
Y
0
1
2
3Si K-edge
SiO2
Si
(a) (b)
460nm
530nm
630nm
530nm
630nm
460nm
44
shell
core
interface
45
Inte
ns
ity
(a
rb.
un
its
)
0
5000
10000
15000
20000
25000
30000
1897.5
1852.5
1847.5
1845.5
1841.5
1831.5
Wavelength (nm)
200 300 400 500 600 700 800
Inte
ns
ity
(a
rb.
un
its
)
0
2000
4000
6000
8000
10000
12000
1831.5
1841.5
1845.5
1847.5
1897.5
1852.5
(a) before HF
(a) after HF
SiNW
hvex
(eV)
hvex
(eV)
450 nm
Photon Energy (eV)1840 1850 1860
TE
Y
0
1
2
3
XEOL and chemistry of SiNW
46
1050104010301020
Energy (eV)
332 nm
OL
W XAS
1050104010301020
Energy (eV)
520 nm
OL
ZB XAS
ZnS hetero-crystalline nano-ribbon
ZnS nw
(wurtzite)
ZnS nw
(zinc blend)
700600500400300
Wavelength (nm)
280 K
10 K Total
800700600500400300
Wavelength (nm)
Total
0-14 ns
520 nm
332 nm
X.-T. Zhou et al., J. Appl. Phys. 98,
024312(2005)
R.A. Rosenberg et al., Appl. Phys. Lett. 87,
253105(2005)
47
XEOL from soft matters
200 300 400 500 600 700 800
0
5
10
15
20
25
30
35
40
Rabbit IGG-FITC Conjugated XEOL
Co
un
ts
Wavelength (nm)
285 eV
400 eV
533 eV
Fluorescein isothiocyanate (FITC) label
FITC conjugated concanavalin A (Con A)
lectin (Con A-FITC) and goat anti-rabbit
immunoglobulin G (IgG) (IgG-FITC)
200 300 400 500 600 700 800
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
2.4
2.6
2.8
FITC label XEOL
285 eV (FITC02)
410 eV (FITC03)
552 eV (FITC01)
Co
un
ts
Wavelength (nm)200 300 400 500 600 700 800
0
5
10
15
20
25
30
35
40
Con A-FITC conjugated XEOL
Co
un
ts
Wavelength (nm)
B
C
D
E
F
G
FITC
Con A
FITC
IGA-
FITC
P.-S. G. Kim et al. Chem. Phys. Lett. 39, 44(2004)